Mayonnaise is America’s favorite condiment, bringing in a total of $401,204,800 in sales annually (see link). There is something about this gooey, spreadable and very versatile condiment that people find irresistible. However, I have never liked mayonnaise and as a kid the mystery of what mayo actually was and what held it all together prevented me from allowing it a place on my sandwich. This post serves as a guide to three popular emulsions: mayonnaise, Hollandaise, and sauce mornay.
What is an emulsion?
An emulsion is a mixture of two incompatible liquids, with droplets of one liquid dispersed in a continuous phase of the other (McGee, p595). Milk, cream, and egg yolks are all examples of natural emulsions although most are commonly used as sauces. The two categories of emulsions are oil-in-water and water-in-oil, distinguished by which is the continuous phase.
Why use egg yolks?
In addition to two incompatible liquids, stable emulsions include a third ingredient, the emulsifier. You may notice that many sauce recipes include egg yolks. This is because egg yolks contain the emulsifier lecithin. Emulsifiers have an oil-like (hydrophobic) end and a water-soluble (hydrophilic end). The sauce is created when the oil droplets are broken up very small and surrounded by an emulsifier. Proteins and other bigger molecules also act as emulsifiers by getting in the way and breaking up smaller molecules, such as oil droplets.
What makes emulsions challenging?
The fact that emulsions contain two substances that don’t want to go together on their own makes them particularly challenging, it is not a spontaneous process. Energy, in the form of mixing, must be added in order to overcome surface tension. If this force is not overcome, or the emulsion separates again, it is “broken”. However, even if the two phases have coalesced, it is possible to recreate the emulsion by adding more emulsifier and continuing to vigorously mix to break apart the oil droplets.
The mayonnaise was created five different ways, incorporating three different mixing techniques and two different types of oil. The three different mixing techniques were using a food processor, by hand and with a salad dressing vessel. The difference was noticeable in the final products. The mayo that was only shaken as if it were a salad dressing did not create a proper emulsion and the food processor was able to. In addition the mayo whisked by hand took a lot of effort to create the emulsion. In order to create a successful emulsion, the oil droplets must be broken up very small and if they are not then the surface tension will not be overcome.
The other change made was substitution extra-virgin olive oil. Extra-virgin olive oil is less acidic and more viscous than regular oil and therefore was able to be broken down into smaller oil droplets. The color was also an indicator of how well the oil droplets were broken down, because bigger droplets reflect light more.
The Hollandaise sauce was also created five different times, using four different fat sources. The different fats (butter, homemade butter, clarified butter, and margarine) changed the recipe by having different concentrations of fat. Regular butter includes milk fats, proteins, and lactose while clarified butter is only milk fat and homemade butter has more buttermilk and water. Therefore the clarified butter thickens the emulsion as it is added while the regular butter than clarified butter thinned the emulsion. The thickness of the clarified butter made it harder to break into small pieces and create the emulsion, resulting in a broken mixture. The margarine acted similar to the other butters.
Sauce Mornay was created three times, varying the cook time and the color of the roux each time. This sauce is different than mayonnaise or hollandaise because it is not created using the lecithin from egg yolks as an emulsifier. Instead, it incorporates milk and cheese. The cooking time changed the flavor of the sauce because of the Millard reactions that occur and change the flavors. They also account for the changing of the color.